Many species in Poa sect. Stenopoa hybridize easily, and have formed a series of morphologically and genetically distinct populations. These are supposed to have been stabilized by apomixis. The situation is made more complex by P. glauca, P. nemoralis, and P. palustris, which are represented by many cytological races of vague taxonomic status. These have hybridized with other species of P. sect. Stenopoa to form agamic complexes, which are supposed to have arisen quite long ago, perhaps during the Pleistocene (Tzvelev, Fl. European Part USSR 1: 117–368. 1974). Four of these have differentiated sufficiently to be treated as the distinct hybridogenous species P. albertii, P. araratica, P. lapponica, and P. urssulensis. Some polytypic species are also accepted. Their subspecies are geographically separated; some may be of hybrid origin, but are close to one parent as result of introgression.

Plants without rhizomes (or at most with poorly developed lateral shoots, or short upward-directed bladeless shoots, or somewhat stoloniferous in riparian forms of Poa palustris); culms usually closely clustered, nodes and internodes not or only slightly compressed, but if compressed then plants not rhizomatous; callus webbed or not

Xeromorphic plants; culm with uppermost node up to 1/3 way up, if up to 1/2 way up and/or plant mesomorphic, then ligule more than 1.5 × blade width; leaf blade firm or soft, folded or flat, 0.5–2.5(–3.5) mm broad, much shorter to infrequently longer than sheath

Plants with 2(or 3) nodes above 1 cm at the base; leaf blade firm or soft and withering in age; uppermost blade usually very narrow and folded, short, usually less than 1/2 as long as sheath to subequal; panicle open to densely spiciform

Plants with 3–5 nodes above 1 cm at the base (if 2, then leaves long, soft, and flat), leaf blade soft and withering with age, never firm, uppermost blades frequently flat, usually more than 1/2 as long as sheath; panicle open or contracted (if contracted, then with blades soft and withering in age), with long erect branches, 1/2 as long as panicle, never dense and spiciform